The main objective of this research is to aid in the design of new antitumor agents based on: 1) the properties of the enzymes thymidylate synthetase, dihydrofolate reductase, their kinetics and interaction with ligands, 2) evaluation of folate analogs as enzyme inhibitors and inhibitors of microbial growth. The following methods are to be employed: proton magnetic resonance, 19F magnetic resonance, 31P magnetic resonance, kinetics, microbiological assay and affinity chromatography.